This invention is in the field of boilers. Specifically it is in the field of control of oxygen scavenger being added to boilers. The control method is based on using fluorometric analytical tools.
It is known that oxygen in aqueous environments in contact with carbon steel results in localized or pitting type corrosion, which can lead to tube failures. Dissolved oxygen in boiler feedwater needs to be low in order to reduce corrosion of the boiler feedwater lines and boiler internals. Make-up water to any boiler circuit is usually saturated with dissolved oxygen. In order to reduce the amount of dissolved oxygen present from the parts per million (hereinafter xe2x80x9cppmxe2x80x9d) level to the desired parts per billion (hereinafter xe2x80x9cppbxe2x80x9d) level, a known piece of equipment, referred to as a deaerator, is installed to remove the dissolved oxygen mechanically.
The remaining oxygen is removed by contacting the boiler make-up water with a chemical scavenger. An additional reason for adding a chemical scavenger is to provide insurance that the oxygen scavenging ability will also be available should there be unwanted leaked oxygen entering the boiler feedwater. The chemical scavenging of trace levels of oxygen from boiler feedwater is done by feeding a sacrificial material, which is readily oxidized in the boiler environment. This sacrificial material is typically referred to as a xe2x80x9cboiler oxygen scavengerxe2x80x9d, or xe2x80x9coxygen scavengerxe2x80x9d for short.
There are many known oxygen scavengers for use in boiler systems. By definition, an oxygen scavenger must be capable of being oxidized. Chemically speaking, oxygen scavengers can be inorganic or organic, and if organic, they can be aromatic or aliphatic. One subset of known oxygen scavengers are the aromatic oxygen scavengers.
Gallic Acid is a known aromatic oxygen scavenger. See U.S. Pat. No. 4,968,438, assigned to Nalco Chemical Company, which is incorporated by reference in its entirety. Claim 1 of this patent is:
xe2x80x9cAn improved method for scavenging dissolved oxygen from waters used to generate steam having a temperature of at least 185xc2x0 F. which comprises treating said waters with at least 0.3 mole of Gallic acid per mole of oxygen contained in said boiler waters.xe2x80x9d
Also see U.S. Pat. No. 4,929,364, assigned to Nalco Chemical Company, which is incorporated by reference herein, in its entirety. Claim 3 of the ""364 patent claims:
xe2x80x9cA method for scavenging dissolved oxygen from waters used to generate steam which comprises treating said waters with at least 0.3 mole of Gallic Acid per mole of oxygen contained in said boiler water using an aqueous concentrate containing at least 1.15 weight percent Gallic Acid, said aqueous concentrate having a pH of at least 8.5, said pH having been adjusted by a water-soluble neutralizing amine of the type used to treat boiler waters, said neutralizing amine being present in sufficient amount to solubilize said Gallic Acid in said waters used to generate steam.xe2x80x9d
Control of boilers and other steam generating equipment is described and claimed in U.S. Pat. No. 5,041,386, assigned to Nalco, which is herein incorporated by reference, in its entirety. In the ""386 patent, concentration cycles, percent life holding time for a component in the boiler and continuous treatment concentrations are monitored or determined in a Boiler System by adding to the feedwater an inert tracer in a predetermined concentration, CI, which reaches a final concentration, CF, at steady state in the boiler and which exhibits a blowdown concentration, Ct, at different points in time. The component is an inert tracer having no significant carryover in the steam, nor significant degradation during boiler cycles. The tracer is monitored by continuously converting a characteristic of its concentration to an analog that may be recorded as a function of time.
It would be desirable to have methods to ensure an optimal amount of aromatic oxygen scavenger is present in a boiler.